In a pig iron production process, different process gases such as offgas from a fluidized bed reduction unit or from a packed bed reduction unit are evolved which need to have entrained solid particles largely removed before being re-used or released into the environment. This takes place in dedusting devices, particularly in dry dedusting devices, wherein the solid particles separated out during dedusting often contain iron or iron compounds which for economic and environmental protection reasons are fed back into the pig iron production process.
For example, in the course of the FINEX® pig iron production process, dedusting of the FINEX® offgas by means of bag filters or hot gas filters produces a dust mass every hour which corresponds to around 2% of the mass of the hourly fine ore charge. The amount of iron contained in this resulting dust mass and/or of iron compounds contained this resulting dust mass is approximately 65%. The amount of carbon contained in this resulting dust mass and/or of carbon compounds contained this resulting dust mass is approximately 6%.
Immediately returning these partly pre-reduced solid particles to a fluidized bed reduction unit, wherein the solid particles are fed back into the fluidized bed reduction unit without prior agglomeration to agglomerates, is problematic in that the grain size of the solid particles is too small—a typical grain size distribution D50 of such solid particles is between 6 and 9 μm—which would result in immediate discharging of the introduced solid particles from the fluidized bed reduction unit. For this reason, according to the prior art the solid particles are normally consolidated into larger entities, in particular agglomerated, prior to introduction into the fluidized bed reduction unit. This agglomeration takes place using separate agglomerating devices. The solid particles are fed into the agglomerating device where they are formed into agglomerates. These agglomerates are then introduced into the fluidized bed reduction unit using suitable charging devices. The disadvantage of this is that separate agglomerating devices are required, which require a large amount of space and the operation of which creates additional costs.
DE 1154817 describes a method of reducing iron ore involving the introduction of finely comminuted iron ore, fluxing agent, fuel, oxygen and/or air into a reaction chamber by means of burners, wherein the reaction chamber is implemented as a smelting furnace. By means of a [ . . . ] mounted in the dome area of the reaction chamber and having its axis perpendicular to the surface of a bath of molten iron and molten slag present in the reaction chamber, the finely comminuted iron ore is fed directly to this surface.
Similarly to DE 1154817, U.S. Pat. No. 2,688,478 discloses a reducing/smelting furnace for reducing and smelting down iron ore as well as producing gas and energy. By means of inlets mounted on the underside of the smelting furnace and just above the molten bath and having their longitudinal axes extending in the direction of the bath surface and into the bath, fine ore and possibly additives are blown into the smelting furnace using an oxygen-containing gas, wherein the injected material is blown directly onto the bath surface where it is smelted down.
Like U.S. Pat. No. 2,688,478, GB 882909 discloses a smelting furnace and a method for smelting down iron ore, wherein fines are introduced into the smelting furnace with the addition of oxygen and a fuel by means of a burner device mounted at the top of the smelting furnace, and the combustion products impinge directly on the surface of the molten metal bath or slag bath present in the smelting furnace and are smelted down.
WO 9815661 shows a method and an apparatus for producing liquid pig iron, wherein fine particulate iron oxide carriers are introduced into the smelting gasification zone of a smelter gasifier by means of a dust burner. Prior to introduction into the smelter gasifier, said fine particulate iron oxide carriers are reduced by means of devices assigned by the apparatus to reduce the iron oxide carriers.
The disadvantage of this is the additional equipment cost/complexity required for the devices for reducing the iron oxide carriers.
WO 02088401 describes a method for producing pig iron in the context of a COREX® process, wherein dust is removed from the export gas drawn off from a smelter gasifier, and the dust together with an oxygen-containing gas and carbonaceous material is returned to the smelter gasifier by means of a dust burner.
WO9802586 discloses a method and a device for producing liquid pig iron, wherein fine-grained and reduced iron ore or dust are introduced into the smelter gasifier by means of burners mounted in the dome region or at the level of the fluidized bed of a smelter gasifier.
WO 9748825 describes a device for producing a molten metal bath by means of a smelter gasifier, wherein partially reduced metal carriers containing fines are introduced into the smelter gasifier, wherein said metal carriers first impinge on a burner-heated collecting device which is disposed centrally in the dome region of the smelter gasifier, are partially melted thereon and then pass by gravity into the smelting gasification zone of the smelter gasifier where they are smelted down.
DE 1086256 describes a device for recovering iron from powdered i.e. fine-grained iron ores by means of fuels. Pre-reduced ore and fine dust from electrical gas cleaning are introduced through inlet nozzles into the smelting chamber together with a fuel and a combustion medium. In the space in front of the inlet nozzles, the introduced components react with one another to form liquid iron and liquid slag which mostly drip down onto the coke bed.
In the case of the above mentioned methods known from the prior art, the fine particulate material is either introduced into a smelting reduction unit where it is smelted down or introduced into a fluidized bed reduction unit after agglomeration in an agglomerating device. A significant disadvantage of the former method is that the fine particulate material is returned to the pig iron production process by introducing the fine particulate material into the smelting reduction unit. The fine particulate material has to be further reduced, i.e. reduction has to be completed, in the smelting reduction unit. However, this has an adverse effect on the smelting and/or gasification process in the smelting gasification zone of the smelting reduction unit. The returning of such fine particulate material to the pig iron production process by introducing the fine particulate material into the smelting reduction unit is therefore restricted in terms of quantity. In other words, with this method known from the prior art it is not possible for any amount of this fine particulate material to be returned to or used in the pig iron production process. The disadvantage of the latter method is that separate agglomerating devices are required. These require much space and create high additional costs.